1. Field of the Invention
The present invention relates to a semiconductor device and a fabrication method thereof. More particularly, the present invention relates to a semiconductor device having at least a double layer type anti-reflective layer used in a photolithography process, and the method of fabricating the dual layer type anti-reflective layer disposed on the semiconductor device.
2. Description of the Related Art
In the process of fabricating semiconductor devices having a design rule of 0.13 xcexcm or less, an ArF laser is used as an exposure light source in a photolithography process. A silicon oxynitride (SiON) layer is generally used as an anti-reflective coating when a KrF laser is used as an exposure light source, since an optimized anti-reflective layer has yet to be developed. However, if a KrF laser is used, intermixing may occur at the boundary between a chemically amplified resist and an anti-reflective layer, resulting in a phenomenon called xe2x80x9cfootingxe2x80x9d in which the lower portion of a photoresist pattern is rounded, rather than rectangular. Also, although organic anti-reflective layers for an ArF laser have been partially developed, optimum layers have yet to be found.
FIGS. 1 and 2 are diagrams showing a semiconductor device employing a typical anti-reflective layer. FIG. 1 is a cross-sectional view taken when a silicon oxynitride layer (SiON) layer is used as an anti-reflective layer. In FIG. 1, bottom layer 52 having a step difference is formed on semiconductor substrate 50, and an underlying layer 54 having a high reflectivity is formed on bottom layer 52. Subsequently, anti-reflective layer 68 formed of silicon oxynitride (SiON) is deposited on the underlying layer 54. Then, a chemically amplified photoresist layer is coated on the anti-reflective layer 68 to then carry out exposure and development, thereby forming a photoresist pattern 56. Here, anti-reflective layer 68 suppresses ripple occurring in the profile of photoresist pattern 56 by the light reflected from the boundary between the photoresist layer and underlying layer 54. Anti-reflective layer 68 also inhibits notching, a phenomenon in which photoresist pattern 56 is narrowed in a xe2x80x9cVxe2x80x9d shape before cutting, thereby accurately controlling the line width in forming a fine pattern. In other words, the anti-reflective layer causes offset-interference with respect to the light reflected from the boundary between the photoresist layer and underlying layer 54.
However, intermixing occurs at the boundary between the silicon oxynitride layer (SiON) used as anti-reflective layer 68 and the chemically amplified photoresist layer so that footing 60 becomes severe. Footing 60 occurs via the reaction of OH and NHx groups in the boundary between anti-reflective layer 68 and the chemically amplified photoresist layer so that the lower portion of the photoresist pattern is not formed at a right angle but is rounded. Here, the OH group is generated from the chemically amplified photoresist layer, and the NHx group is generated from the SiON layer.
FIG. 2 is a graph showing the reflectivity versus the change in thicknesses of an anti-reflective layer when silicon oxynitride (SiON) is used as the anti-reflective layer. Here, the refractive index (n) for the photoresist layer and the anti-reflective layer is 1.8, and the extinction coefficient (k) for the photoresist layer and the anti-reflective layer is 1. The extinction coefficient represents the degree to which an arbitrary light ray is transmitted through a layered material. For this example, a silicon layer is used as underlying layer 54. When the thickness of anti-reflective layer 68 is about 200 angstroms, the reflectivity is about 5%.
A conventional method of fabricating semiconductor devices in which a double layer type anti-reflective layer is used is disclosed in U.S. Pat. No. 5,733,712, entitled xe2x80x9cResist Pattern Forming Method Using Anti-Reflective layer, Resist Pattern Formed, and Method of Etching Using Resist Pattern and Product Formedxe2x80x9d, issued on Mar. 31, 1998. This patent discloses a technology in which a silicon oxynitride (SiON) layer and a metal layer are used as a double layer type anti-reflective layer. This patent fails to take into consideration intermixing at the boundary between the chemically amplified photoresist layer and a silicon oxynitride layer (SiON).
To solve the above problems, the present invention preferably provides a semiconductor device having a double layer type anti-reflective layer, which has a low reflectivity even when an ArF laser is used as an exposure light source. A further feature of the present invention is the suppression of intermixing at the boundary between a photoresist layer and an anti-reflective layer.
Still another feature of the present invention is to provide a method of fabricating a semiconductor device having the double layer type anti-reflective layer.
Accordingly, to achieve the above features of the present invention, a semiconductor device including an underlying layer having a high reflectivity is formed on a semiconductor substrate. A double layer type anti-reflective layer formed of a nitride layer and a layer formed using only hydrocarbon-based gas is formed on the underlying layer, and a photoresist layer is formed on the double layer type anti-reflective layer.
According to a preferred embodiment of the present invention, the double layer type anti-reflective layer is preferably a layer in which a nitride layer and a layer formed using only hydrocarbon-based gas are sequentially formed, or a layer in which a layer formed using only hydrocarbon-based gas and a nitride layer are sequentially formed.
Preferably, the nitride layer has a refractive index of between 2 and 3 with respect to an exposure light source, and has an extinction coefficient of between 0.01 and 0.21.
It is desirable that the layer formed using only the hydrocarbon-based gas be an amorphous carbon layer, containing an additive agent which is one of oxygen, tin, lead, silicon, fluorine and chlorine. Also, the amorphous carbon layer preferably has a refractive index of between 1.4 and 2.5 with respect to an exposure light source, and the amorphous carbon layer preferably has an extinction coefficient of between 0.01 and 0.21.
According to another aspect of the present invention, a method of forming a semiconductor device having a double layer type anti-reflective layer is disclosed. The method includes forming an underlying layer having a high reflectivity on a semiconductor substrate, depositing a nitride layer as a first anti-reflective layer on the underlying layer, depositing a layer formed using only hydrocarbon-based gas as a second anti-reflective layer on the first anti-reflective layer, and coating a photoresist pattern on the second anti-reflective layer.
Preferably, in the step of forming the underlying layer, the material of the underlying layer is selected from the group consisting of tungsten, tungsten silicide (WSix), titanium silicide (TiSix), aluminum and aluminum alloy. Also, in the step of depositing the layer formed of a hydrocarbon-based gas, the hydrocarbon-based gas is preferably selected from the group consisting of methane, ethane, propane, butane, acetylene, propene and n-butane.
In the step of forming the second anti-reflective layer, the second anti-reflective layer may be formed by plasma enhanced chemical vapor deposition (PECVD). Also, after forming the second anti-reflective layer, the method may include performing one step selected from the group consisting of annealing, RF plasma treatment, E-beam treatment, and curing, to increase the density of the layer.
According to the present invention, in the photolithography process in which an ArF laser is used as an exposure light source, the thickness of an anti-reflective layer is appropriately adjusted, to lower the reflectivity. Also, the stability of a layer material of an amorphous carbon layer used in the present invention, in which only hydrocarbon-based gases are used, can prevent intermixing occurring at the boundary between the photoresist layer and the anti-reflective layer. Further, in the photolithography process using an ArF laser in which a relatively thin photoresist layer is employed, the double layer type anti-reflective layer according to the present invention can function as a hard mask which is advantageous in an etching process. Also, since the layer formed by using only the hydrocarbon-based gas according to the present invention can be removed by a process of removing a photoresist without a separate removal process, the fabrication process can be simplified.